GLENWOOD SPRINGS, Colo.—Big rocks are crashing onto busy highways in western Colorado canyons, marking an early start to the annual boulder season.

Boulders tumble down on Interstate 70 in Glenwood Canyon and Colorado 82 in the Roaring Fork Valley every spring as melting snow loosens the canyon walls.

Colorado State Patrol Capt. Rich Duran said the season is starting early this year and could get bad in March and April because of heavy snowfall this winter, leading to extra runoff.

This week, falling boulders crashed through a concrete median divider on Colorado 82. No one was hurt.

Duran said boulders sometimes fall onto moving vehicles, and in past years, crashing boulders have led to deaths.

But Duran said it’s more common for a motorist to hit a boulder that’s already lying on the road. That has happened at least five times in the area so far, but no one was seriously hurt, he said.

Dave Stanley, service manager at Glenwood Shell, said he’s seen eight or nine vehicles this year with damage averaging $400 to $500 collisions with rocks on highways. Mostly, the work involves repairing broken wheels and damaged oil or transmission pans.

Not all damage is from hitting rocks. Some cars trying to dodge a boulder sometimes hit a guardrail or another car.

“It created a lot worse damage than just going ahead and running over the rock,” Stanley said. “You never know what (drivers) are going to do when a rock falls in front of them.”